This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. This project focuses on the development and use of transmission electron microscopy in characterizing membrane protein-protein complexes. We will develop an automated assay to image, select, and classify membrane protein complexes in terms of their aggregation state, size, conformational state and domain arrangement. One goal is to develop a more systematic understanding of the effect of detergents and lipids on the stability and conformation of membrane proteins and their complexes in order to help optimize crystallization efforts. A more ambitious goal is to map out individual protein domains in order to better understand the interactions between proteins in a complex that might be conformationally or structurally heterogeneous. This low resolution information can be combined with high-resolution models of individual subunits or subcomplexes, derived from X-ray and NMR studies, in order to develop a more detailed understanding of the protein- protein interactions within complexes.